Globoid worm fluid-flow machines

ABSTRACT

The invention relates to machines such as compressors or pumps of the kind including an hourglass worm meshing with a toothed pinion. It is known to make the pinion of metal coated with a resilient material such as plastic rigidity fixed to the surface of the metallic pinion. According to the invention the metal pinion is covered with a plastic lining having teeth which engage the threads of the worm and prevent the metal teeth of the pinion from engaging those threads. The plastic lining is permitted a slight shifting about its average position respectively to the metal pinion.

1 Jan. 29, 1974 United States Patent 1191 Zimmern' m mm mm wmm Hm wmm 1%G22 i 540 r Wyn mm 1 m E1 60 mm 6 3 1 mm 135 in rs 23 PA e .m m& n W Inm By a n m m U me L :lr. F Ze d me m be. 0 m W e m B BDF m O m B t 0 mLA v GM .m H M 5 U [22] Filed: July 3, 1972 Attorney, Agent, orFirm-Young and Thompson Appl. No.: 268,890

Foreign Application Priority Data July 30, 1971 or pumps of the kindincluding an hourglass worm France..............................71127968 meshing with a toothed pinion. It is known to make 52 us.418/153, 74/425, 74/458, the Pinion of metal Coated with a resilientmaterial such as plastic rigidity fixed to the surface of the me-418/195 F0lc 5/02, F16h 1/16 tallic pinion. According to the inventionthe metal pinion is covered with a plastic lining having teeth whichengage the threads of the worm and prevent the metal [51] Int. [58]Field of Searchmm..." 418/152, 153, 178, 195;

74/425, 458, DIG. 10

teeth of the p1n1on from engaging those threads. The plastic lining ispermitted a slight shifting about its average position respectively tothe metal pinion.

References Cited UNITED STATES PATENTS 7 Claims, 10 Drawing Figures1,785,140 Morris 418/195 PATENIE JANwBM SHEET 1 [1F 2 4 at ZPATENTEDJANZS I974.

SHEET 2 [If 2 vLlull GLOBOID WORM FLUID-FLOW MACHINES Thisinventionrelates to globoid worm (or hourglass worm) fluid-flowmachines, such as compressors, pumps, or expansion units.

It is known that such machines, as for instance described in French Pat.No. 1,331 ,998 and US. Pat. No. 3,55l,082, have a rotor consisting of agloboid worm with several threads co-operating with at least onegaterotor consisting of a metal pinion whose teeth are en gaging thethreads of the rotor in order to achieve compression or expansion of theenclosed gaseous medium.

Also, it is known after US. Pat. No. 2,716,861 that the above-mentionedpinions can be completely coated with some flexible and relativelyresilient material, such as synthetic rubber or plastic, such coatingbeing rigidly attached all over the surface of the pinions.

However, experience tends to show two kinds of drawbacks in suchsystems.

First, rapid erosion will develop on the sides of the pinion teeth, insome cases, where they come against the threads of the rotor. This israther unexpected, since said pinions are not subjected to any brakingreaction, and remain perfectly free to move between the threads of therotor. Such erosion is observed particularly in compressors, even withoil lubrication. It is still worse if water lubrication is attempted,which indeed is specially interesting for oil-free production ofcompressed air. I

Second, such known arrangements are relatively noisy. For instance, acompressor or vacuum pump having a swept volume of 4,000 liters perminute will produce a noise level of some 85 to 90 decibels at adistance of 1 meter.

The object of the invention is to overcome such difficulties, and moreprecisely to provide machines having a seriously extended operatinglife, practically suppressing all erosion cffects, even with waterlubrication, and seriously reducing the noise level, by some to decibelsin the aforementioned case.

In accordance with the invention, there is provided a globoid wormfluid-flow machine, such as a compressor, a pump or expansion unit,comprising a rotor with several threads, at least .one toothed metalpinion whose teeth are co-operating with said threads, a casing at leastpartly covering said rotor and where passageways have been cut for thepath of said teeth, inlet and outlet apertures for the fluid on eachside of said rotor, high pressure apertures being located near saidpinions, wherein the width of the teeth of the metal pinion is smallerthan the distance between two contiguous threads of the rotor, at leasta part of that face of the pinion which is subjected to the fluidpressure being covered with a plastic material lining, the parts of thislining covering the teeth of the pinion being wider than the latterteeth, in order to have said parts in touch with the threads of therotor, avoiding contacts of the teeth of the metal pinion against saidthreads, means being provided for a slight shifting of the lining aroundits average position on the pinion.

Further features and advantages of the invention will become apparentfrom the following description of several embodiments taken asnon-limitative examples, and illustrated in the-appended drawings, inwhich:

FIG. 1 is a diametral sectional view ofa first embodiment ofa pinion,covered with a plastic liner, according to the invention.

FIG. 2 is a plan view of the pinion of FIG. 1.

FIG. 3 is a sectional view of FIG. 2, along line X-X.

FIG. 4 is a sectional view, comparable to FIG. 3, of a conventionalpinion tooth.

FIG. 5 is a sectional view of an alternative embodiment of the pinionshown in FIGS. 1 to 3.

FIG. 6 is a sectional and diametral view of a second embodiment ofapinion, with its lining according to the invention.

FIG. 7 is a partial perspective of the pinion of FIG. 6.

FIG. 8 is a sectional view along Y-Y' line of FIG. 7. FIG. 9 is apartial plan view of another embodiment of the lining of the pinionshown in FIG. 2.

FIG. 10 is a partial perspective view of another embodiment of thepinion of FIG. 6 with its lining.

A first embodiment of a pinion according to the invention is shown inFIG. 1, indiametral sectional view,

- the teeth being arranged in a plane.

This pinion is part of a compressor comprising a casing 1, in which amulti-threaded rotor (not shown) is arranged to revolve around axis 2,in the direction of arrow 3. This pinion, arranged to revolve aroundaxis 4, is formed of a metal part 5, preferably of steel or cast iron,supported in casing l by roller-bearings 6 and thrust-bearing 8.

That face of the pinion which is subjected to the fluid pressure islined with a sheet of plastic material 9, attached to the pinion 5 witha metal plug 10 driven into the metal body of the pinion, and adjustedwithin a hole of the plastic liner with a clearance going frompractically nil up to a few hundredths of one millimeter.

In the latter case, it will be noted that the plastic liner can not belifted off its metal support, since it would then come against a flatface 11 of the casing, the corresponding gap in operation between liner9, when resting on the pinion metal body 5, and the opposite face 11 ofthe casing being very thin, usually less than ten hundredths of onemillimeter.

Therefore, parts 5 and 9 do not need any positive assembly means, suchas nuts or alike.

FIG. 3 shows the arrangement of the plastic liner on its metal support,at the pinion teeth level.

Metal teeth such as 5a of pinion S are narrower than the distancebetween flanks 14a, 14b, of two adjoining threads of the rotor. Also,teeth such as 9a, formed in the plastic liner to cover metal teeth 5a,are wider than the latter, and the flanks of the plastic teeth havefaces with different slopes 12a, 13a and 12b, 13b in order to adaptthemselves, in a known manner, to angular changes in the threads of therotor, when the pinion is rotating relatively to the latter.Intersections 15a, 15b between such slopes are corresponding to actualcontact lines between flanks 12a, 12b of plastic teeth 9a and threads14a, 14b.

Due to their narrower dimension, as compared with plastic teeth 9a,metal teeth 5a do not extend as far as the latter sideways, and theirflanks 16a, 16b can not therefore get against thread faces 14a, 14b,even when plastic teeth are slightly shifted, relatively to their metalsupport.

It will be noted that metal teeth 5a are quite thicker than plasticteeth 9a, having to bear fluid pressure, under plastic teeth of onlylittle stiffness.

The following dimensions can be indicated, for a typical embodiment ofthe kind just described. On a millimeter diameter pinion, there areeleven teeth, each 35 mm long and 25 mm wide. In order to sustain loadscorresponding to 7 bar compressed air, the metal support of the plasticteeth is 12 mm thick at the root of the teeth, and 6 mm thick at thetip, the plastic liner being 6 mm thick.

Slopes 13a, 13b of the plastic teeth extend over flanks 16a, 16b of themetal teeth by 0.5 millimeter, therefore allowing teeth 9a to shiftaround their average position by some 0.2 to 0.3 millimeter. Indeed, theinvention provides such attachment means, for the resilient liner 9 onmetal pinion 5, as to permit a slight shifting of the liner around itsaverage position rela tively to this pinion.

The aforementioned shift can be obtained just through the mere flexibleproperties of the plastic material. Using such plastics as polyamid l 1,known under the trademark Rilsan, or materials formed of alternatelayers of cotton and asbestos fibers coated with phenolic resins andknown under the trademarks Celoron, Synthane, or Ferrobestos, atransverse shifting of the plastic teeth was observed relatively totheir metallic support, reaching one tenth of a millimeter undersideways applied loads of a few kilogrammes.

This shifting possibility is distinctive with respect to suchconventional structure, as described in US. Pat. No. 2,716,861 where aresilient material 17, such as rubber or polyamid 11 already mentioned,is applied in moulded form around metal teeth 18, completely surroundingthem.

Practically, such a conventional structure was found unsatisfactory,since serious erosion effects would tend to develop after only a fewhundred hours of operation, rapidly leading to a complete destruction ofthe machine. Moreover, machines built with such technology produce aserious noise-of some 85 to 90 decibels at a distance of 1 meter, in thecase of a compressor or a vacuum pump having a swept volume of 4,000liters per minute, with two pinion teeth engaged on their both flanks,according to French Patent 1,331,998.

This invention, on the contrary, provides for machines having theadvantage of being very quiet, in identical conditions with a noiselevel lower by some decibels, besides a complete freedom of erosion. Anadditional advantage lies in the fact that, even if erosion isartificiallystarted, say for instance with a high braking reactionapplied on the pinion, the resulting wear will not tend to keep growingas formerly, once the artificial braking is interrupted. On thecontrary, erosion effects will tend to remain unchanged in continuedoperation.

Without affecting at all the scope of the invention, these seriouslyimproved'results can be explained as follows.

Normally, when engaging the rotor, the pinion can be considered as amovable shutter, only subjected in rotation to such loads as derivedfrom the friction in the bearings, which is negligible. The piniontherefore behaves as a completely loose gear, free to shake or vibratearound its average position between the threads of the rotor. Suchvibrations involve angular accelerations, with resulting impact effectson both sides of each pinion tooth against the threads of the rotor.This approach of the problem is indeed sustained by the fact thattypical wear scratches have been found with conventional pinions on bothflanks of the rotor threads, and not only on that side which actuallydrives the pinion. The vibrations can be produced by small initialdefects in the geometry of the machine.

In the structure covered by the invention, such small defects are notsuppressed. But, considering above mentioned results, one would thinkthat only the plastic liner of the pinion tends to vibrate around itsaverage position, while its support, in other words the metal pinion,keeps turning smoothly at constant speed. Alone, the plastic liner has avery much lower inertia than the solid parts described in reference toFIG. 4; it is also more flexible. Finally, initial vibrations of thesame amplitude will produce reduced impact effects where the kineticenergy is affected by the same ratio as between the respectiveproperties of inertia and flexibility of the parts.

Whereas a resilient material is severely eroded by such impact effects,when it is solidly and completely attached to its metal support, nomeasurable erosion appears when this material is connected to its metalsupport with the flexible arrangement provided by the invention.

Though this is not absolutely necessary for the aboveindicated results,a more accurate control of the linear angular shifting around itsaverage position and of the pull-back forces involved is obtained withan alternate arrangement of the attachment of the plastic liner on themetal pinion, as shown in FIG. 5.

In this alternate arrangement, there is a head 19 on plug 10a, with around collar 22 where a ring 20 is inserted. Made for instance ofrubber, ring 20 is applied against the wall of a bore 21, formed throughplastic liner 9.

With this arrangement, pull-back forces acting on liner 9 can beadjusted with various values of the ring thickness, its initialcompression being defined by diametral differences between bore 21 andthe edge 22 of the plug head 19. Respective diameters of these two partscan be chosen with such values as to maintain the maximum possibleangular shift of plastic teeth 9a, even after accidental destruction ofring 20, below the clearance provided by different widths of plasticteeth 13 and metal teeth 16 respectively, thus avoiding any possiblecontact of these meatal teeth against the rotor threads.

Another alternate embodiment of the invention is shown in FIGS. 6 to 8,corresponding to pinions with their teeth arranged on a cylindricalsurface, according to French Patent No. 1,586,832.

In FIG. 6, a casing 23 is housing a threaded rotor (not shown) which isarranged to revolve around axis 24, in the direction indicated by arrow25. A metal pinion 27, supported by needle-bearings 29, 30, in casing23, is revolving around a shaft 28.

In this particular embodiment, fluid pressure is applied on the insideface of the cylindrical part of the toothed pinion 27, a plastic liner31 being arranged within this hollow cylindrical pinion 27, withattachment plug 32.

FIG. 7 shows a metal tooth 27a covered by a plastic tooth 31a, theirrelative arrangement appearing in sectional view in FIG. 8. Flanks 36a,36b of the rotor threads are bearing against bevel-edges 35a, 35b oneach side of the plastic tooth, respectively at the intersection ofslopes 33a, 34a and 33b, 34b.

As with other shapes of the pinion, high levels of erosion and noisehave been observed, when the pinion is formed with a metal bodycompletely surrounded with plastic material. But wear and noise areseriously reduced with a metal pinion having a flexibly attached liner,according to the invention.

This remarkable improvement is even more apparent in this particulararrangement, since a cylindrical pinion of the kind described has muchmore inertia than flat pinions which were previously described.

Naturally, in a compressor where the pinions would have their outsideface, instead of the inner one, subjected to fluid pressure, therelative arrangement of the plastic liner over its metal pinion would bereversed, the liner then covering-the outside face of the metal pinioninstead of the inside.

The plastic liner 31 can be elastically attached to the metallic pinion,for instance by insertion of a resilient ring, as shown in FIG. 5 forthe case of a plane pinion.

In cases when the shift between the liner and the metallic pinion isobtained through the flexibility of the plastic material of the liner,said flexibility can be increased by creating a region of reducedcross-sectional area close to the base of the teeth of the liner, asshown in FIG. 9 for a plane liner and FIG. 10 in the case of a liner fora pinion having its teeth on a cylindrical sur face.

Teeth 9a or 31a are formed with notches 51, 61 which determine regions52, 62 having a smaller crosssectional area than that of the adjacentregions. Regions 52, 62 are located beyond the zone of the teeth whichengages the flanks of the rotor thread and contribute to increase theshift of the teeth for a given lateral stress.

Such a feature is especially interesting for machines such as describedin French Patents 1,331,998 and 1,586,832 wherein only one tooth engagesthe threads along all its height. The other teeth engage the threadsonly towards their end, where the shifting possiblity brought about bythe notches is maximum.

Of course, the invention is not limited to such embodiments as justdescribed, and various alternate arrangements can be introduced withoutdeparting from the scope of the invention.

What I claim is:

1. In a globoid or hourglass worm fluid flow machine,

such as a compressor, pump or expansion unit, com-- prising amulti-threaded hourglass rotor, at least one toothed metal pinion whoseteeth cooperate with said threads and have one face subjected to thefluid pressure, and a casing at least partially covering said rotor; theimprovement in which the width of the teeth of the metal pinion issmaller than the distance between two contiguous threads of the rotor, aplastic material lining covering at least part of said face of thepinion which is subjected to the fluid pressure, the parts of thislining which cover the teeth of the pinion being wider than said teeth,in order to have said parts in touch with the threads of the rotor andto avoid contact of the teeth of the metal pinion with said threads, andmeans to allow a slight shift of said lining around its average positionon the pinion.

2. A machine according to claim 1, wherein said means to allow a slightshift of said lining comprises means mounting said lining on said pinionfor limited sliding movement on and relative to said teeth.

3. A machine according to claim 1, wherein that face of the teeth ofthe'lining which is subjected to the fluid pressure is arranged in aplane.

4. A machine according to claim 1, wherein that face of the teeth of thelining which is subjected to the fluid pressure is formed in cylindricalarrangement.

5. A machine according to claim 1, wherein the plastic material liningis bound to the metal pinion with a flexible attachment.

6. A machine according to claim 5, wherein the metal pinion bears atleast one protruding plug housed within a hollow part of the plasticliner, a resilient ring being arranged around the plug of the pinion,between the walls of the hollow part of the plastic liner and said plug.

7. A machine according to claim I, wherein those parts of the linerwhich cover the pinion teeth have a region of reduced cross-sectionalarea, said region being located beyong those zones of said parts of theliner which engage the threads of the rotor.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 378878ADated January 7 Inventor(s) Bernard Zlmmern It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

On the Cover Sheet, in item [21] "268,890" should read 268,905

Signed and sealed this 6th day of May 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officerand Trademarks F ORM PC3-1050 (IO-69) USCOMM-DC 60376-P69 u.s covs umnnPRINTING enact: a 93 o

1. In a globoid or hourglass worm fluid flow machine, such as acompressor, pump or expansion unit, comprising a multi-threadedhourglass rotor, at least one toothed metal pinion whose teeth cooperatewith said threads and have one face subjected to the fluid pressure, anda casing at least partially covering said rotor; the improvement inwhich the width of the teeth of the metal pinion is smaller than thedistance between two contiguous threads of the rotor, a plastic materiallining covering at least part of said face of the pinion which issubjected to the fluid pressure, the parts of this lining which coverthe teeth of the pinion being wider than said teeth, in order to havesaid parts in touch with the threads of the rotor and to avoid contactof the teeth of the metal pinion with said threads, and means to allow aslight shift of said lining around its average position on the pinion.2. A machine according to claim 1, wherein said means to allow a slightshift of said lining comprises means mounting said lining on said pinionfor limited sliding movement on and relative to said teeth.
 3. A machineaccording to claim 1, wherein that face of the teeth of the lining whichis subjected to the fluid pressure is arranged in a plane.
 4. A machineaccording to claim 1, wherein that face of the teeth of the lining whichis subjected to the fluid pressure is formed in cylindrical arrangement.5. A machine according to claim 1, wherein the plastic material liningis bound to the metal pinion with a flexible attachment.
 6. A machineaccording to claim 5, wherein the metal pinion bears at least oneprotruding plug housed within a hollow part of the plastic liner, aresilient ring being arranged around the plug of the pinion, between thewalls of the hollow part of the plastic liner and said plug.
 7. Amachine according to claim 1, wherein those parts of the liner whichcover the pinion teeth have a region of reduced cross-sectional area,said region being located beyong those zones of said parts of the linerwhich engage the threads of the rotor.